Synthesis of two metal-porphyrin frameworks assembled from porphyrin building motifs, 5, 10, 15, 20-tetrapyridylporphyrin and their base catalyzed property

Opening catalytically active sites in metal organic frameworks is an issue of fundamental importance for the development of effective and efficient catalysts. In this work, we first reported two metal metalloporphyrin–organic frameworks (MMPFs) with unoccupied pyridine groups as base catalysts. The reaction of Mn(II) and Co(II) with 5,10,15,20-tetrapyridylporphyrin produces two different metal metalloporphyrin–organic frameworks, {(MnTPyP)]·H₂O}_n (MMPF-Mn) and (CoTPyP)]_n (MMPF-Co) (TPyP = 5,10,15,20-tetrapyridylporphyrin) under hydrothermal conditions. These two MMPFs have been fully characterized by single-crystal X-ray diffraction, powder XRD, elemental analysis and thermogravimetry (TG). MMPF-Mn displays a 3D network with a nbo topology, large and open hexagonal channels, MMPF-Co reveals a 1D single zigzag chain architecture. Interestingly, both MMPFs have a high thermal stability and opening basic pyridine group, which have been tested for the base catalyzed Knoevenagel condensation reaction. The catalytic study has demonstrated that MMPF-Mn catalysts having exposed pyridine group within 1D channel displayed an excellent performance for Knoevenagel condensation reaction. When MMPF-Mn was recycled four times, its catalytic activity remained with an inconspicuous decrease. We attribute MMPF-Mn showing a better performance than MMPF-Co to its active sites being aligned in extra-large cavity with an interior diameter of 20 Å.